Prop RPM dropping over time

[Dwaldvogel]

I have a '62 M20C. The hartzel 2 blade adjustable pitch prop, on an O-360, RPM has been decreasing over the last several flights. I've adjusted the prop 1/2 a turn, in order to get 2675RPM, twice now but after one or two additional flights 2500RPM is the most that I can get. I think it may be the governor. Any other suggestions?

Also, has anyone removed a governor from an M20C as it looks like quite a job. Any suggestions?

Thanks!

[carusoam]

There are a few wear parts that can be overhauled in the governor...

I had mine done in a 65C. It is a mechanic job to remove and send out. If you haven't had it done in a couple thousand hours, it's a good time to consider that....

Welcome to MooneySpace...

Best regards,

-a-

[N201MKTurbo]

To remove the governor, first remove the oil filter/screen. Remove the air pump and accessary drive. Then remove the right mag. Remove the prop cable and the oil line to the front of the engine. Remove any heater ducts and electrical connections that are in the way. Remove all eight nuts from the governor and the drive pad. Work the governor and drive out of the engine together. Pull the drive about half way out and tilt upwards. The governor will now come off the drive and after that the drive will come out. Re-assemble in the reverse order.

 

The other option is to remove the engine from the mount. With the above method you can have the governor out in about 30 minutes. (unless the oil line is being a Bi***)

[Cody Stallings]

How long has it been sense the prop was off for a flush or O/H? The cylinder of a propeller that has been in service for many yrs can get a build up of sludge on top of the piston, which restricts the pitch change rods travel. When it does it makes the prop not go all the way to fine pitch(highrpm)...... If its the gov sending uncommanded oil to the propeller, then you could not adjust it out with the propellers low pitch stop...Our props are pressure to increase pitch, an blade morph an spring to decrease. All but the 305 Rocket operate this way.

Just my opinion, but I think the problem is on the front of the motor ,not the back.

[takair]

Are you sure it is not cable rigging? A broken cable mount under the cowl or something restricting full travel on that end?

[FloridaMan]

Have you verified that your tach is accurate?

[Marauder]

Have you verified that your tach is accurate?

That is certainly one thing I would look at too. My tach cable was replaced when I was having the avionics work done and it was never right again. It started with oscillating between 2,500 and 2,700 and then it dropped to 2,500 for the max and I never saw 2,700 again. I had the tach replaced with an EI unit and all is well again.

[HRM]

My prop and gov had not been touched for 30 some years. I started having trouble getting it to hold speed. I had the prop redone and the governor. Night and day difference. The other thing I noticed was that on run up there was a noticeable delay when I exercised the prop--now it is almost instantaneous.

[Cody Stallings]

Horizon P1000 took care of my tach issues.... An optical tach payed on the dash would be a good idea , if you haven't already done it.

[Dwaldvogel]

Thanks for all the suggestions! I'm going to check the tach first although it was overhauled about 200 hours and 10 years ago. I had the prop off to replace the seals 50 hours ago and found some corrosion on the forks requiring replacement. Everything else in the prop looked ok. Pulling the gov off will be my last option.